1. Field of the Invention
The present invention relates to an illumination system and a projection system, and more particularly, to a compact illumination system, which realizes a color image without a color wheel, and a projection system employing the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional projector includes a light source 100, a first relay lens 102, a color wheel 105, a fly eye lens 107, a second relay lens 110, a display device 112, and a projection lens system 115. The first relay lens 102 focuses a beam emitted from the light source 100. The color wheel 105 divides incident light into three color beams (R, G, B). The fly eye lens 107 makes uniform the beams which have passed through the color wheel 105. The second relay lens 110 focuses the beams which have passed through the fly eye lens 107. The display device 112 forms a color image using the R, G, B beams which are sequentially incident via the color wheel 105. The projection lens system 115 enlarges the color image formed by the display device 112 and projects the enlarged color image on a screen 118.
The light source 100 may be a xenon lamp, a metal-halide lamp, or an ultra high performance (UHP) lamp, all of which emit a large amount of unnecessary infrared rays and ultraviolet rays and thus generate a large amount of heat. A cooling fan (not shown) is used to cool the light source 100, but generates noise. Also, these lamps have a wide emission spectrum and thus a narrow color gamut. Thus, these lamps can emit a narrow range of colors, and have poor color purity and a short lifespan.
In a conventional projection system, a driving motor (not shown) rotates the color wheel 105 at a high speed to illuminate the display device 112 with R, G, B colors, thereby creating a color image. R, G, B filters are symmetrically disposed on the color wheel 105 and the color wheel 105 rotates during formation of a picture. During each rotation of the color wheel 105, only one of the colors is passed, thus, ⅔ of the light is lost. Also, predetermined gaps are formed at the boundaries between the colors of the color wheel 105. Thus, loss of light occurs at the boundaries between the colors of the color wheel 105.
Moreover, since the color wheel 105 mechanically rotates at a high speed, it is noisy and unstable. Also, it is difficult for the color wheel 105 to go faster than a certain speed because of the mechanical limitations of the driving motor. Thus, a color breakup phenomenon occurs. Furthermore, the color wheel 105 is expensive to manufacture.